Combined wafer production method with laser treatment and temperature-induced stresses

ABSTRACT

The present invention relates to a method for the production of layers of solid material. The method according to the invention comprises at the very least the steps of providing a solid body ( 2 ) for the separation of at least one layer of solid material ( 4 ), generating defects by means of at least one radiation source, in particular a laser, in the inner structure of the solid body in order to determine a detachment plane along which the layer of solid material is separated from the solid body, and applying heat to a polymer layer ( 10 ) disposed on the solid body ( 2 ) in order to generate, in particular mechanically, stresses in the solid body ( 2 ), due to the stresses a crack propagating in the solid body ( 2 ) along the detachment plane ( 8 ), which crack separates the layer of solid material ( 4 ) from the solid body ( 2 ).

The present invention relates to a method for the production of layersof solid material according to the subject matter of claim 1 and to awafer produced by this method (claim 13).

In many technical domains (e.g. microelectronic or photovoltaictechnology) materials, such as e.g. silicon, germanium or sapphire, areoften needed in the form of thin discs and plates (so-called wafers). Asstandard, such wafers are currently produced by sawing from an ingot,relatively large material losses (“kerf loss”) occurring. Since thesource material used is often very expensive, great efforts are beingmade to produce such wafers with less material consumption and so moreefficiently and inexpensively.

For example, with the currently normal methods almost 50% of thematerial used is lost as “kerf loss” when producing silicon wafers forsolar cells alone. Considered globally, this corresponds to an annualloss of more than 2 billion euros. Since the cost of the wafer makes upthe greatest percentage of the cost of the finished solar cell (over40%), the cost of solar cells could be significantly reduced by makingappropriate improvements to the wafer production.

Methods which dispense with the conventional sawing and can separatethin wafers directly from a thicker workpiece, e.g. by usingtemperature-induced stresses, appear to be particularly attractive forthis type of wafer production without kerf loss (“kerf-free wafering”).These include in particular methods as described e.g. inPCT/US2008/012140 and PCT/EP2009/067539 where a polymer layer applied tothe workpiece is used in order to produce these stresses.

In the aforementioned methods the polymer layer has a thermal expansioncoefficient that is higher by approximately two orders of magnitude incomparison to the workpiece. Moreover, by utilising a glass transition arelatively high elasticity modulus can be achieved in the polymer layerso that sufficiently large stresses can be induced in the polymer layerworkpiece layer system by cooling in order to enable the separation ofthe wafer from the workpiece.

Upon separating a wafer from the workpiece, in the aforementionedmethods polymer still adheres to a respective side of the wafer. Thewafer bends here very strongly towards this polymer layer, and thismakes it difficult to execute the separation in a controlled manner, andmay lead e.g. to variations in the thickness of the separated wafer.Moreover, the strong curvature makes subsequent processing difficult andmay even lead to the wafer shattering.

When using the methods according to the previous prior art, the wafersproduced generally have respectively larger thickness variations, thespatial thickness distribution often showing a pattern with four-foldsymmetry. The total thickness variation seen over the entire wafer(“total thickness variation”, TTV) is often more than 100% of theaverage wafer thickness when using the previous methods (a wafer with anaverage thickness of, for example, 100 micrometres, that is e.g. 50micrometres thick at its thinnest point and 170 micrometres thick at itsthickest point, has a TTV of 170−50=120 micrometres, which correspondsto a total thickness variation of 120% relative to its averagethickness). Wafers with these strong thickness variations are unsuitablefor many applications. Moreover, with the most frequently occurringfour-fold thickness distribution patterns, the regions with the greatestvariations unfortunately lie in the middle of the wafer where they causethe greatest disruption.

Moreover, in the method according to the current prior art, undesirableoscillations in the layer systems involved occur during the breakpropagation upon separation, and these oscillations have a negativeimpact upon the development of the break front and may in particularlead to significant thickness variations of the separated wafer.

In addition, with the previous methods it is difficult to ensurereproducibly good heat contact over the entire surface of the polymerlayer. Locally insufficient heat contact may, however, lead toundesirable significant local temperature variations in the layer systemdue to the low thermal conductivity of the polymers used, and this onits part has a negative impact upon the controllability of the stressfields produced and so upon the quality of the wafers produced.

Furthermore, a method for the separation of semiconductor materials bymeans of light-induced boundary surface decomposition and apparatusesproduced in this way, such as structured and free-standing semiconductorlayers and components, is known from publication DE 196 40 594 A1. Themethod according to DE 196 40 594 A1 includes the illumination ofboundary surfaces between the substrate and the semiconductor layer orbetween semiconductor layers, by means of which the light absorption onthe boundary surface or in an absorption layer provided for this purposeleads to material decomposition.

The choice of boundary surface or semiconductor layer which can becaused to decompose is made by choosing the light wavelength and thelight intensity, the irradiation direction or the insertion of a thinsacrificial layer during the material production. The disadvantage ofthis method is that high doses of energy have to be used in order todestroy whole layers, due to which the energy requirement, and so thecosts of the process are very high.

Furthermore, publications EP000002390044B1, EP000001498215B1,EP000001494271B1 and EP000001338371B1 disclose a method in which thelaser is used for the vertical separation of workpieces.

Furthermore, laser-supported methods for generating areas of damagewithin a wafer are known. With a focussed laser multiphoton excitationsare thereby achieved at depth, by means of which it is possible to causedamage at depth without causing damage upon material entry.

Typically, lasers with an ns pulse duration (nanosecond pulse duration)are used here so that a strong interaction of the heated material andthe laser can occur. Typically, this happens by means of a photon/photoninteraction which has a clearly higher absorption than the multi-photonexcitation.

This type of method is known, for example, from Ohmura et. al. (Journalof Achievements in Materials and Manufacturing Engineering, 2006, vol17, p. 381 ff). The wafer treatment proposed by Ohmura et al. serves togenerate crack directing lines by generating defects within the wafer,as can be partially provided by isolating wafer elements of a waferplate. The defects generated by this method extend in a verticaldirection here, by means of which the connection structure between theindividual wafer elements is subjected to longitudinal weakenings atright angles to the main surface of the wafer elements. Theselongitudinal weakenings have extensions of >50 μm.

The advantage utilised in order to isolate wafer elements, namely thegeneration of extensions with a vertical extension of >50 μm preventsthe application of this type of defect generation to methods for thesplitting off of one or more wafer layers from a solid body. On the onehand, with the generation of these longitudinal defects distributed overthe wafer surface, a material layer is produced within the solid bodywhich can only be used to direct cracks, but is unsuitable forsubsequent use, and so constitutes waste. On the other hand, this wastemust be removed, e.g. by a polishing process, by means of which therewould be additional cost. It is therefore the object of the presentinvention to provide a method for the production of layers of solidmaterial or solid bodies that enables the inexpensive production ofsolid plates or uneven solid bodies with a desired thicknessdistribution, the vertical damage being minimised by the crack plane.

It is therefore the object of the present invention to provide a methodfor the production of layers of solid material that enables theinexpensive production of solid plates or wafers with an even thickness,in particular with a TTV of less than 120 micrometres. According toanother aspect of the present invention the object is to provide amethod for the production of one or more layers of solid material inwhich a crack propagation plane is generated by means of a laser withina solid body, the individual defects forming the crack propagation planehaving a vertical extension of less than 50 μm.

The aforementioned object is achieved by a method according to claim 1for the production of layers of solid material. This method preferablycomprises at least the steps of providing a workpiece or a solid bodyfor the separation of at least one layer of solid material, generatingdefects by means of at least one radiation source, in particular alaser, in particular an fs laser or femtosecond laser, in the innerstructure of the solid body in order to determine a detachment planealong which the layer of solid material is separated from the solidbody, providing a receiving layer for holding the layer of solidmaterial on the solid body, applying heat to the receiving layer inorder to generate, in particular mechanically, stresses in the solidbody, due to the stresses a crack propagating in the solid body alongthe detachment plane, which crack separates the layer of solid materialfrom the solid body.

This solution is advantageous because by virtue of the radiation sourcethe detachment layer or defect layer can be generated in the solid bodyby means of which the crack is managed or directed during the crackpropagation, and this makes it possible to produce very small TTVs, inparticular smaller than 200 micrometres or 100 micrometres or smallerthan 80 micrometres or smaller than 60 micrometres or smaller than 40micrometres or smaller than 20 micrometres or smaller than 10micrometres or smaller than 5 micrometres, in particular 4, 3, 2, 1micrometres. Exposing the wafer to rays thus creates in a first step atype of perforation within the solid body along which, in a second step,the crack propagation takes place or along which the layer of solidmaterial is separated from the solid body.

Additional advantageous embodiments are the subject matter of thefollowing description and/or the sub-claims.

According to one preferred embodiment of the present invention the laserhas a pulse duration of less than 10 ps, particularly preferably of lessthan 1 ps and at best of less than 500 fs.

According to one preferred embodiment of the present invention thestresses for detaching the layer of solid material are generated by thesolid body by applying heat to the receiving layer, in particular apolymer layer. The application of heat preferably constitutes cooling ofthe receiving layer or polymer layer at or below ambient temperature andpreferably below 10° C. and particularly preferably below 0° C. and morepreferably below −10° C. Extremely preferably the cooling of the polymerlayer takes place such that at least part of the polymer layer, which ispreferably made of PDMS, undergoes a glass transition. In thisconnection the cooling can be cooling to below −100° C. which can bebrought about e.g. by means of liquid nitrogen. This embodiment isadvantageous because the polymer layer contracts depending on thetemperature change and/or undergoes a glass transition, and transfersthe forces thus produced to the solid body, by means of which mechanicalstresses can be generated in the solid body which lead to the initiationof a crack and/or crack propagation, the crack first of all propagatingalong the first detachment plane in order to split off the layer ofsolid material.

According to one preferred embodiment of the present invention the solidbody is disposed on a holding layer for holding the solid body, theholding layer being disposed on a first level surface portion of thesolid body, the first level surface portion of the solid body beingspaced apart from a second level surface portion of the solid body, thepolymer layer being disposed on the second level surface portion, andthe detachment plane being aligned parallel to the first level surfaceportion and/or to the second level surface portion or being generated inparallel.

This embodiment is advantageous because the solid body is disposed atleast partially and preferably entirely between the holding layer andthe polymer layer, by means of which the stresses for generating cracksor propagating cracks can be introduced into the solid body by means ofone of these layers or by means of both of the layers.

According to another preferred embodiment of the present invention atleast or precisely one radiation source for providing the radiation tobe introduced into the solid body is configured such that the raysirradiated by it generate the defects at predetermined locations withinthe solid body. This embodiment is advantageous because by means of aradiation source, in particular by means of a laser, one can generatedefects in the solid body with extreme precision.

In particular, there are two applications for the method, in thefollowing called “wafering” and “thinning”. With “wafering” the methodis generally used to detach a thick layer from an even thickersemiconductor block, typically a wafer (with the industry-specificthicknesses) from an ingot. With “thinning” the method is used to splitoff a very thin layer from a wafer, and this corresponds to today'sgrinding process, but with the advantage that the material that is notrequired remains intact and can be reused. It is complicated to make aclear separation between “thinning” and “wafering” because e.g. the“thinning” can also take place by acting on the rear side of a wafer sothat a thin layer is produced, but the laser penetrates deeply into thematerial.

For the case of “thinning”:

According to another preferred embodiment of the present invention theradiation source is set up such that the rays irradiated by it in orderto generate the detachment plane penetrate into the solid body to adefined depth, in particular <100 μm. Preferably, the detachment planeis formed in parallel, spaced apart from an outer and preferably levelsurface of the solid body. Preferably, the detachment plane is less than100 micrometres and preferably less than 50 micrometres and particularlypreferably less than or precisely 20, 10, 5 or 2 micrometres away fromthe level surface of the solid body within the solid body. Therefore,the detachment plane is preferably made in the form of a plane generatedfrom defects, the defects being formed spaced apart by less than 100micrometres and preferably by less than 50 micrometres and particularlypreferably by less than 20, 10 or 2 micrometres from the level surfaceof the solid body within the solid body.

For the case of “wafering”:

According to another preferred embodiment of the present invention theradiation source is set up such the rays irradiated by it in order togenerate the detachment plane penetrate into the solid body to a defineddepth, in particular >100 μm. Preferably, the detachment plane is formedin parallel, spaced apart from an outer and preferably level surface ofthe solid body. Preferably, the detachment plane is formed spaced apartby more than 100 micrometres and preferably by more than 200 micrometresand particularly preferably by more than 400 or 700 micrometres from thelevel surface of the solid body within the solid body. Therefore, thedetachment plane is preferably made in the form of a plane generated bydefects, the defects being formed spaced apart by more than 100micrometres and preferably by more than 200 micrometres and particularlypreferably by more than 400 or 700 micrometres from the level surface ofthe solid body within the solid body.

According to another preferred embodiment of the present invention thesolid body is exposed to a predetermined wavelength and/or output, thepredetermined wavelength preferably being adapted to the respectivematerial or substrate. This embodiment is advantageous because the sizeof the defect can be influenced by the wavelength and/or the output.

According to another preferred embodiment of the present invention thesolid body comprises silicon and/or gallium or perovskite, and thepolymer layer and/or the holding layer are made at least partially, andpreferably entirely, or by more than 75% of polydimethylsiloxane (PDMS),the holding layer being disposed on an at least partially level surfaceof a stabilisation device which is made at least partially of at leastone metal. The stabilisation device is preferably a plate, in particulara plate that comprises aluminium or is made of the latter. Thisembodiment is advantageous because by means of the stabilisation deviceand the holding layer the solid body is defined or held securely, bymeans of which the stresses can be generated very precisely in the solidbody.

According to another preferred embodiment of the present invention thestresses in the solid body can be set up or generated such that thecrack initiation and/or the crack propagation can be controlled in orderto generate a topography of the surface that is produced in the crackplane. Therefore, the stresses can preferably be generated in differentregions of the solid body such as to be of different strengths, at leastfrom time to time. This embodiment is advantageous because bycontrolling the crack initiation and/or the crack development, thetopography of the layer of solid material that is generated or separatedcan advantageously be influenced.

According to another preferred embodiment of the present invention thedefects determine at least one crack directing layer, the at least onecrack directing layer being of a form different from a level form. Thissolution is advantageous because the layers of solid material generatedor the solid bodies generated can have a form different from a levellayer. Therefore, no longer are only level layers formed or generated,but also three-dimensional bodies, from a workpiece by means of crackpropagation. On the basis of the production method solid bodies producedin this way have a very advantageous surface that only needs to bereworked to a small extent or not at all. Thus e.g. optical elements,such as e.g. a prism or a lens can be produced in a one-stage ormulti-stage, in particular two- or three-stage splitting process.

Therefore, according to a preferred embodiment of the present inventionthe form of the crack directing layer has at least partially the contourof a three-dimensional object, in particular of a lens or a prism.

According to one preferred embodiment of the present invention thedefects are generated by means of a defect generation apparatus or theradiation source, the defect generation apparatus being configured suchthat the defects are generated in the workpiece a constant distance awayfrom the defect generation apparatus, the workpiece and the defectgeneration apparatus being inclined relative to one another such thatthe defects generated by the defect generation apparatus are generatedin the crack directing layer, the defect generation apparatus and theworkpiece only being re-positioned two-dimensionally in relation to oneanother during the defect generation. The defect generation apparatus istherefore preferably re-positioned in relation to the workpiece, or theworkpiece is re-positioned in relation to the defect generationapparatus, or the defect generation apparatus and the workpiece are bothre-positioned in relation to one another.

This embodiment is advantageous because the radiation source or thedefect generation device need only be repositioned in order to generatedefects, and no modification needs to be made to the defect generationapparatus, and in particular no changed defect introduction depth needsto be determined or set.

According to another preferred embodiment the defects are generated bymeans of a defect generation apparatus or the radiation source, thedefect generation apparatus being configured such that the defects aregenerated in the workpiece a distance away from the defect generationapparatus that changes from time to time, a modification of the defectgeneration apparatus being brought about at least from time to timedepending on the distance between the defect generation apparatus andthe defect to be generated, in particular a changed defect introductiondepth being determined and set up. This embodiment is advantageousbecause preferably, no incline apparatus need be provided in order toincline the workpiece.

The solid body preferably comprises a material or a material combinationof one of the main groups 3, 4 and 5 of the periodic table of theelements, such as e.g. Si, SiC, SiGe, Ge, GaAs, InP, GaN, Al2O3(sapphire), AlN. Particularly preferably, the solid body has acombination of elements occurring in the third and the fifth group ofthe periodic table. Conceivable materials or material combinations hereare e.g. gallium arsenide, silicon, silicon carbide etc. Furthermore,the solid body can comprise a ceramic (e.g. Al2O3—aluminium oxide) or bemade of a ceramic, preferred ceramics here being e.g. perovskiteceramics (such as e.g. ceramics containing Pb, O, Ti/Zr) in general andlead magnesium niobates, barium titanate, lithium titanate, yttriumaluminium garnet, in particular yttrium aluminium garnet crystals forsolid body laser applications, SAW (Surface Acoustic Wave) ceramics,such as e.g. lithium niobate, gallium orthophosphate, quartz, calciumtitanate, etc. in particular. Therefore, the solid body preferablycomprises a semiconductor material or a ceramic material, orparticularly preferably the solid body is made of at least onesemiconductor material or a ceramic material. Furthermore, it isconceivable for the solid body to comprise a transparent material or tobe made of or to be produced partially from a transparent material suchas e.g. sapphire. Additional materials that can be considered as a solidmaterial here on their own or in combination with another material aree.g. “wide band gap” materials, InAlSb, high temperaturesuperconductors, in particular rare earth cuprates (e.g. YBa2Cu3O7).

According to another preferred embodiment of the present invention theradiation source or part of the radiation source is in the form of afemtosecond laser (fs laser). This solution is advantageous because byusing an fs laser the vertical propagation of the defective material isminimised. By using an fs laser it is possible to introduce defects inthe workpiece very precisely and to generate them in the latter. Thewavelength and/or the energy of the fs laser are preferably to be chosendependently upon the material.

According to another preferred embodiment of the present invention theenergy of the radiation source, in particular of the laser beam, inparticular of the fs laser, is chosen such that the damage propagationwithin the solid body or within the crystal is smaller than three timesthe Rayleigh length, preferably smaller than the Rayleigh length andparticularly preferably smaller than one third of the Rayleigh length.

The wavelength of the laser beam, in particular of the fs laser, ischosen according to another preferred embodiment of the presentinvention such that the absorption of the solid body or of the materialis less than 10 cm⁻¹ and preferably less than 1 cm⁻¹ and particularlypreferably less than 0.1 cm⁻¹.

According to another preferred embodiment of the present invention theindividual defects respectively result from multiphoton excitationbrought about by the radiation source, in particular the laser, inparticular an fs laser.

Furthermore, the invention relates to a wafer that is produced by amethod according to any of claims 1 to 12.

Furthermore, the subject matter of publications PCT/US2008/012140 andPCT/EP2009/067539 is made complete by referring to the subject matter ofthe present patent application. Likewise, the subject matter of all ofthe other patent applications also submitted by the applicant on theapplication date of the present patent application and relating to thedomain of the production of layers of solid material are in theirentirety included in the subject matter of the present patentapplication.

Other advantages, aims and properties of the present invention areexplained by means of the following description of the attached drawingsin which the wafer production according to the invention is shown as anexample. Components or elements of the wafer production according to theinvention which in the figures correspond, at least substantially withregard to their function, can be identified here by the same referencesigns, these components or elements not having to be numbered orexplained in all of the figures.

Individual or all of the illustrations of the figures described beloware preferably to be considered as design drawings, i.e. the dimensions,proportions, functional relationships and/or arrangements shown by thefigure or figures preferably correspond precisely or preferablysubstantially to those of the apparatus according to the invention or ofthe product according to the invention.

The figures show as follows:

FIG. 1a a diagrammatic construction for generating defects in a solidbody;

FIG. 1b a diagrammatic illustration of a layer arrangement beforeseparating a layer of solid material from a solid body;

FIG. 1c a diagrammatic illustration of a layer arrangement afterseparating a layer of solid material from a solid body;

FIG. 2a a first diagrammatically illustrated variation for generatingdefects by means of light waves;

FIG. 2b a second diagrammatically illustrated variation for generatingdefects by means of light waves; and

FIG. 3 a diagrammatic illustration of the detachment plane.

FIG. 1a shows a solid body 2 or a substrate that is disposed in theregion of a radiation source 18, in particular a laser. The solid body 2preferably has a first level surface portion 14 and a second levelsurface portion 16, the first level surface portion 14 preferably beingaligned substantially or exactly parallel to the second level surfaceportion 16. The first level surface portion 14 and the second levelsurface portion 16 preferably delimit the solid body 2 in a Y directionthat is preferably aligned vertically or perpendicularly. The levelsurface portions 14 and 16 preferably extend respectively in an X-Zplane, the X-Z plane preferably being aligned horizontally. Furthermore,it can be gathered from this illustration that the radiation source 18irradiates rays 6 onto the solid body 2. The rays 6 penetrate by adefined depth into the solid body 2 depending on the configuration andgenerate a defect at the respective position or at a predeterminedposition.

FIG. 1b shows a multi-layered arrangement, the solid body 2 containingthe detachment plane 8 and being provided in the region of the firstlevel surface portion 14 with a holding layer 12 which is in turnpreferably overlaid by an additional layer 20, the additional layer 20preferably being a stabilisation device, in particular a metal plate. Apolymer layer 10 is preferably disposed on the second level surfaceportion 16 of the solid body 2. The polymer layer 10 and/or the holdinglayer 12 are preferably made at least partially and particularlypreferably entirely of PDMS.

FIG. 1c shows a state after a crack initiation and subsequent crackdirecting. The layer of solid material 4 adheres to the polymer layer 10and is or can be spaced apart from the remaining part of the solid body2.

FIGS. 2a and 2b show examples of the generation, shown in FIG. 1a , of adetachment plane 8 by introducing defects into a solid body 2 by meansof light rays.

Therefore, the present invention relates to a method for the productionof layers of solid material. This method according to the inventionincludes at the very least the steps of providing a solid body 2 for theseparation of at least one layer of solid material 4, generating defectsby means of at least one radiation source, in particular at least onelaser, in particular at least one fs laser, in the inner structure ofthe solid body in order to determine a detachment plane along which thelayer of solid material is separated from the solid body, and applyingheat to a polymer layer 10 disposed on the solid body 2 in order togenerate, in particular mechanically, stresses in the solid body 2, dueto the stresses a crack propagating in the solid body 2 along thedetachment plane 8, which crack separates the layer of solid material 4from the solid body 2.

Therefore, FIG. 2a shows diagrammatically how defects 34 can begenerated in a solid body 2, in particular in order to generate adetachment plane 8 by means of a radiation source 18, in particular oneor more lasers, in particular one or more fs lasers. Here the radiationsource 18 emits radiation 6 with a first wavelength 30 and a secondwavelength 32. The wavelengths 30, 32 are matched to one another here orthe distance between the radiation source 18 and the detachment plane 8to be generated is matched such that the waves 30, 32 convergesubstantially or precisely on the detachment plane 8 in the solid body2, by means of which a defect is generated at the point of coinciding 34as a result of the energies of the two waves 30, 32. The generation ofdefects can take place here by means of different or combineddecomposition mechanisms such as e.g. sublimation or chemical reaction,the decomposition being able to be initiated here e.g. thermally and/orphotochemically.

FIG. 2b shows a focussed light ray 6, the focal point of whichpreferably lies in the detachment plane 8. It is conceivable here forthe light ray 6 to be focussed by one or more focusing bodies, inparticular a lens/lenses (not shown). In this embodiment the solid body2 is multi-layered in form and preferably has a partially transparent ortransparent substrate layer 3 or material layer that is preferably madeof sapphire or comprises sapphire. The light rays 6 pass through thesubstrate layer 3 onto the detachment plane 8 which is preferably formedby a sacrificial layer 5, the sacrificial layer 5 being exposed toradiation such that partial or complete destruction of the sacrificiallayer 5 is brought about thermally and/or photochemically in the focalpoint or in the region of the focal point. It is also conceivable forthe defects for the generation of the detachment layer 8 to be generatedin the region of or precisely on a boundary surface between two layers3, 4. It is therefore also conceivable for the layer of solid material 4to be generated on a support layer, in particular a substrate layer 3,and for a detachment plane 8 for the detachment or separation of thelayer of solid material 4 to be able to be generated by means of one ormore sacrificial layers 5 and/or or by means of the generation ofdefects in a boundary surface, in particular between the layer of solidmaterial 4 and the support layer.

FIG. 3 shows a detachment plane 8 which has regions with differentconcentrations of defects 82, 84, 86. It is conceivable here for aplurality or regions with different concentrations of defects to form adetachment plane 8, it also being conceivable for the defects 34 in thedetachment plane 8 to be distributed substantially or exactly evenlyover the surface. The different concentrations of defects per area canbe of the same level or of different levels. Preferably, a firstincreased concentration of defects constitutes a crack initiationconcentration 82 which is preferably generated in the region of the edgeor extending towards the edge or adjacent to the edge. In addition oralternatively, a crack directing concentration 84 can be formed suchthat the crack separating the layer of solid material 4 from the solidbody 2 can be controlled or regulated. Furthermore, in addition oralternatively, a concentration at the centre 86 is generated whichpreferably makes a very level surface possible in the region of thecentre of the solid body 2. Preferably, the crack directingconcentration 84 is made to be partially or entirely annular orencircling, and so preferably partially and particularly preferablyentirely encircles the centre of the solid body 2 or the layer of solidmaterial 4. Furthermore, it is conceivable for the crack directingconcentration 84 to decrease step by step, constantly or fluently in adirection passing from the edge of the solid body 2 and towards thecentre of the solid body 2. Furthermore, it is conceivable for the crackdirecting concentration 84 to be formed in bands and homogeneously orsubstantially or exactly homogeneously.

Therefore, the method according to the invention preferably includes thefollowing steps:

Providing a workpiece for the detachment of at least one layer of solidmaterial and/or at least one solid body, the workpiece having at leastone exposed surface, generating defects within the workpiece by means ofa radiation source, in particular a laser, in particular an fs laser, ora defect generation apparatus, the defects determining a crack directinglayer, applying or generating a receiving layer on the exposed surfaceof the workpiece such as to form a composite structure, tempering thereceiving layer in order to generate stresses within the workpiece, thestresses bringing about crack propagation within the workpiece, by meansof the crack propagation a layer of solid material being separated fromthe workpiece along the crack directing layer.

LIST OF REFERENCE SIGNS

-   2 solid body-   3 substrate-   4 layer of solid material-   5 sacrificial layer-   6 radiation-   8 detachment plane-   10 polymer layer-   12 holding layer-   14 first level surface portion-   16 second level surface portion-   18 radiation source-   20 stabilisation device-   30 first radiation portion-   32 second radiation portion-   34 location of the defect generation-   82 crack initiation concentration-   84 crack directing concentration-   86 concentration at the centre-   X first direction-   Y second direction-   Z third direction

1. A method for the production of layers of solid material, comprisingat the very least the following steps: providing a solid body (2) forthe separation of at least one layer of solid material (4), generatingdefects by means of at least one radiation source (18), in particular alaser, in the inner structure of the solid body in order to determine adetachment plane along which the layer of solid material is separatedfrom the solid body, providing a receiving layer (10) for holding thelayer of solid material (4) on the solid body (2), applying heat to thereceiving layer (10) in order to generate, in particular mechanically,stresses in the solid body (2), due to the stresses a crack propagatingin the solid body (2) along the detachment plane (8), which crackseparates the layer of solid material (4) from the solid body (2). 2.The method according to claim 1, characterised in that the at least oneradiation source (18) for providing the radiation (6) to be introducedinto the solid body (2) is configured such that the rays (6) irradiatedby it generate the defects at predetermined locations within the solidbody (2).
 3. The method according to claim 2, characterised in that theradiation source (18) is set up such that the rays (6) irradiated by itin order to generate the detachment plane (8) penetrate into the solidbody (2) to a defined depth of less than 200 μm, preferably of less than100 μm and more preferably of less than 50 μm and particularlypreferably of less than 20 μm.
 4. The method according to claim 2,characterised in that the radiation source is set up such that the rays(6) irradiated by it in order to generate the detachment plane (8)penetrate into the solid body (2) to a defined depth of more than 100μm, preferably of more than 200 μm and more preferably of more than 400μm and particularly preferably of more than 700 μm.
 5. The methodaccording to any of the preceding claims, characterised in that thesolid body (2) is disposed on a holding layer (12) for holding the solidbody (2), the holding layer (12) being disposed on a first level surfaceportion (14) of the solid body (2), the first level surface portion (14)of the solid body (2) being spaced apart from a second level surfaceportion (16) of the solid body (2), the polymer layer (10) beingdisposed on the second level surface portion (16), and the detachmentplane (8) being aligned parallel to the first level surface portion (14)and/or the second level surface portion (16).
 6. The method according toany of the preceding claims, characterised in that the solid body (2)comprises silicon carbide and/or gallium arsenite and/or a ceramicmaterial, and the receiving layer is made of a polymer layer (10), thepolymer layer and/or the holding layer (12) being made at leastpartially of PDMS, the holding layer (12) being disposed on an at leastpartially level surface of a stabilisation device (20) which is made atleast partially of at least one metal.
 7. The method according to any ofthe preceding claims, characterised in that the stresses in the solidbody (2) can be set up such that the crack initiation and/or the crackpropagation can be controlled in order to generate a pre-determinedtopography of the surface that is produced in the crack plane.
 8. Themethod according to any of the preceding claims, characterised in thatthe radiation source is a femtosecond laser.
 9. The method according toany of the preceding claims, characterised in that the radiation source,in particular the laser, has a pulse duration of less than 10 ps,preferably of less than 1 ps and particularly preferably of less than500 fs.
 10. The method according to any of the preceding claims,characterised in that the energy of the laser beam, in particular of thefemtosecond laser, is chosen such that the damage propagation within thesolid body is smaller than 3 times the Rayleigh length, preferablysmaller than the Rayleigh length and particularly preferably smallerthan one third of the Rayleigh length.
 11. The method according to anyof the preceding claims, characterised in that the wavelength of thelaser beam, in particular of the femtosecond layer, is chosen such thatthe absorption of the solid body is less than 10 cm⁻¹ and preferablyless than 1 cm⁻¹ and particularly preferably less than 0.1 cm⁻¹.
 12. Themethod according to any of the preceding claims, characterised in thatthe individual defects respectively result from multiphoton excitationbrought about by the femtosecond laser.
 13. A wafer, produced by amethod according to any of claims 1 to 12.